When fuel is added to a fuel reservoir, such as the gasoline tank of an automobile from a conventional gas dispenser apparatus such as the dispensing nozzle of a gasoline dispenser, gasoline vapor is displaced from the gasoline tank. If the vapor is not collected in some way, it will be released into the atmosphere. Due to the large number of automobile refuelings, such releases of fuel vapor constitute a significant hazard to the environment, particularly in heavily populated areas. Releases of these vaporst which are composed of volatile organic compounds (VOC's) such as hydrocarbons, are presently the subject of significant and increasing federal and local regulation.
In an effort to guard against the release of volatile organic compounds to the environment, several systems have been designed to collect the vapors displaced from automobile gasoline tanks during refueling. One such system called the "balance" system provides a rubber boot which surrounds the dispenser nozzle and forms a seal &round an automobile gasoline tank filler pipe. This system relies on the volumetric displacement of the vapor by the fluid transferred through the nozzle to the gasoline tank to force the vapor through the boot, through a connecting conduit, and back into a fuel storage tank. A bulky and cumbersome nozzle is required to effect the necessary seal at the filler pipe. If a perfect seal is not made, then vapor can leak to the atmosphere instead of being returned to the storage tank.
To mitigate the need for a cumbersome dispenser nozzle design and to increase the collection efficiency of the dispenser, systems have been designed wherein vapor collection at the nozzle is assisted by a vacuum pump. An example of such a system is disclosed in U.S. Pat. No. 5,040,577 to Pope, the disclosure of which is hereby incorporated by reference. A problem that can arise with a pump assisted system is that the pump can have a tendency to pressurize the fuel storage tank and associated piping. If the volume of vapor collected at the nozzle and conveyed into the fuel storage tank by the vapor pump is more than the volume of liquid fuel dispensed from the nozzle, the pressure in the fuel storage tank will be increased. In the current art of vapor pump assisted vapor recovery systems that use bootless nozzles, a ratio of vapor recovered versus product delivered greater than 1:1 is required to achieve desired recovery efficiency at the filler pipe.
Both pressurization and depressurization of the fuel storage tank can have detrimental effects. When a fuel storage tank has an internal pressure which is greater than the ambient pressure, there is an increased tendency for fuel and/or vapor to leak from gaps in the piping or the tank. Because many tanks are located underground, it is difficult both to detect leaks and to repair leaks. If the fuel storage tank becomes highly over-pressurized, there is a danger that the structural integrity of the tank may be threatened and even a danger of catastrophic breach of fuel containment. Additionally, over-pressurization of the fuel storage tank lessens the efficiency of the vacuum assist pump by creating a greater pressure differential between the nozzle and the fuel storage tank.
In order to solve the foregoing problems of over-pressurization, several devices and methods have been developed to vent fuel storage tanks. It will be understood that a large portion of gas vented from the fuel storage tank will consist of volatile organic compounds. Regulations exist and will likely be made more stringent which limit the amount of VOC's that may be expelled into the atmosphere by such vents. Several techniques have been developed to meet these regulations. One such technique is disclosed in U.S. Pat. No. 4,118,170 to Hirt. The invention of Hirt involves burning the vapor vented. The danger of this technique is obvious, and the technique is presently not allowed in many areas. An alternate technique is to cool the vapor and return the condensed vapor to the tank as liquid. This technique is relatively expensive as it requires a refrigeration device.
Therefore, there exists a need for an efficient, cost-effective apparatus and method for removing volatile organic compounds and other pollutants from gas vented from a fuel storage tank. Furthermore, there exists a need for such a method and apparatus which can be retrofitted to existing fuel storage tanks.